Scubapro67
Contributor
Having moved over to more tech diving, I've become accustomed to carrying an AL40 as a deco bottle with the doubles set up (for one long tech profile), or as a bail-out with my HP120 single tanks (when doing recreational profiles). I used to use a pony bottle with the single tank set up, but now much prefer clipping off the AL40 under an arm while diving. Better access, more gas than I had with the pony, and I can hand it off to a buddy if needed. I'd use the doubles all the time for redundancy, but only have HP100s doubled - tends to be too little gas for two dives to the depths I go (100-120ft), plus the charters I use won't go with two sets of doubles (no way I'm doubling the HP120s!).